The present invention relates to a process for manufacturing a spray urethane elastomer. More particularly it relates to a process for manufacturing a solventless spray urethane elastomer prepared from a prepolymer component obtained by a specific formulation and a resin component by use of two components high pressure spray machine.
The conventional manufacturing processes for spraying urethane elastomers include, for example, a solvent dilution process (in Adiprene Bulletin by Du Pont de Nemours) which comprises dissolving a prepolymer having a terminal isocyanato group and a highly active aromatic amine curing agent such as diphenylmethanediamine and the like in a solvent separately, and coating by use of the conventional two components spray machine (pressure: about 70 Kg /cm.sup.2); a process which comprises diluting, in a solvent, and mixing the above prepolymer and a low active aromatic amine curing agent such as 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA) and the like, followed by spraying within a pot life by use of a high pressure one component spray machine (see Japanese Patent Application Laid Open No. 17430/74 by MITSUI TOATSU CHEMICALS, INC.); a process using a high boiling solvent to maintain it in a coated product; a process comprising reacting a partial prepolymer with a mixture of a high molecular weight polyol and a low molecular weight polyol (see Japanese Patent Application Laid-Open Nos. 134077/75 and 147329/75 by MITSUI TOATSU CHEMICALS, INC.); and the like.
The above process using the solvent raises environmental pollution problems due to the solvent, raises thermal energy loss problems due to forced heat curing in the case of thick-coating, and raises problems of developing a large amount of foam from the coated product in the case of thick-spraying at one time because of the need to evaporate the solvent from the coated product. The process which uses the high boiling solvent to prevent foams from developing and allows the solvent to remain in the coated product, raises such problems as the solvent is lost when the coated product is used over a long period of time due to migration, evaporation, elution into rainwater and the like, resulting in deterioration of the coating taking place along with cracking, shrinkage, etc.
A process, in which coating is carried out thinly and repeatedly, has such a drawback that it takes a long period of time to accomplish the coating.
A process, in which, for example, a carbodiimide modified liquid diphenylmethane diisocyanate (hereinafter diphenylmethane diisocyanate is referred to as MDI.) or a partial prepolymer of MDI is reacted with a mixture of a high molecular weight polyol and a low molecular weight polyol to prepare a coated product, has such a drawback that the low molecular weight polyol is so highly hydroscopic as to result in a competitive reaction between the hydroxyl group and moisture, in being easily foamed, in developing pinholes, craters and the like on the coated product, and in reducing the specific gravity and strength of the coated product.
The above processes all have such drawbacks as reduction in density of the coated product, and consequently a deterioration in physical properties, deterioration in surface properties, etc., because foaming due to moisture in the air and foaming due to moisture caused by hydroscopicity of the polyol component, etc. are not completely controlled.
The conventional processes for manufacturing urethane elastomer include such ones as cast molding, millable polyurethane process, thermoplastic molding, etc. It was very difficult for the above processes to apply to a lining in order to impart abrasion resistance, etc. to a surface having a complicated configuration.